An inbred rat model system using transplantable Morris hepatomas (5123tc, 7777, 3924a, and 9098) has been studied to evaluate serological methods for the detection of tumor specific transplantation antigens. We have used the 3M KCl extraction method to prepare tumor specific extracts. We have immunized animals with these extracts against a subsequent challenge with liver tumor cells. Only occasional immunoprotection has resulted from these experiments. Attempts at preparing a monospecific antiserum against the tumor specific transplantation antigen by xenogeneic immunization have been unsuccessful. We are at present assessing whether the presence of the tumor specific antigens can be demonstrated using in vitro techniques. Additional studies are currently under investigation to evaluate to what extent antibodies to the tumor cells or to the tumor specific antigen extracts can be demonstrated in "immune" animals.